South Fork Snoqualmie River Gravel Removal Study

King County, Washington

About the study

This study of the South Fork Snoqualmie River characterizes the existing sediment accumulation and flooding conditions and evaluates the effectiveness of gravel removal for flood reduction in the South Fork Snoqualmie River from the North Bend Boulevard (Bendigo) Bridge upstream approximately 1.6 river miles to near the I-90 Bridges.

King County monitors sediment levels in this part of the South Fork Snoqualmie River to determine whether sediment accumulations are causing an adverse effect on flood hazards. If monitoring indicates an adverse effect on flood hazards, then potential sediment management actions can be considered, including gravel removal.

This study found that gravel removal could reduce flood hazards at certain locations with some degree of effectiveness over a limited amount of time, while incurring considerable impacts and costs. A permanent or long-term solution to river flooding along this study reach will require measures beyond the gravel removal that was analyzed in this study. A comprehensive consideration of potential flood risk reduction projects is being coordinated for the South Fork Snoqualmie and Middle Fork Snoqualmie Rivers through the efforts of the King County Flood Control District, and should include consideration of gravel removal.